build: Depend on flutter in workspace package to fix renovate

[provokateurin]

Renovate fails upgrading dependencies in the workspace package because it thinks it's a pure dart package: #2181 (comment)
The check for that is not great, but we can simply satisfy it for now: https://github.com/renovatebot/renovate/blob/2818808f28ad18be6ac2644b2bc036b8dd236a23/lib/modules/manager/pub/artifacts.ts#L42

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.61%. Comparing base (b1a31fb) to head (22f017b).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2926   +/-   ##
=======================================
  Coverage   28.61%   28.61%           
=======================================
  Files         374      374           
  Lines      144735   144735           
=======================================
  Hits        41417    41417           
  Misses     103318   103318           

Flag	Coverage Δ		*Carryforward flag
account_repository	98.47% <ø> (ø)
cookie_store	99.48% <ø> (ø)
dashboard_app	96.05% <ø> (ø)
dynamite	31.05% <ø> (ø)
dynamite_end_to_end_test	62.44% <ø> (ø)
dynamite_runtime	85.40% <ø> (ø)
interceptor_http_client	97.18% <ø> (ø)
neon_dashboard	96.05% <ø> (ø)		Carriedforward from b1a31fb
neon_framework	59.23% <ø> (ø)
neon_http_client	92.38% <ø> (ø)
neon_notifications	100.00% <ø> (ø)		Carriedforward from b1a31fb
neon_rich_text	100.00% <ø> (ø)
neon_storage	94.66% <ø> (ø)
neon_talk	99.45% <ø> (ø)		Carriedforward from b1a31fb
nextcloud	24.22% <ø> (ø)
notifications_app	97.43% <ø> (ø)
notifications_push_repository	98.11% <ø> (ø)
sort_box	90.90% <ø> (ø)
talk_app	98.84% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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